1. Field of the Invention
The present invention relates to an actuator to control flow of fluid flowing in a channel, and more particularly to an actuator provided with a seal structure to prevent leakage of fluid.
2. Description of the Related Art
A shutoff valve is used in a channel of a gas supply equipment, and a flow control valve is used for control of gas flow and for switching control of refrigerant gas channel for air-conditioning. The flow control valve is driven by an actuator such that a rotary motion of a motor shaft is converted into a linear motion of a valve by means of a pinion gear or a screw structure.
FIG. 5 is a cross sectional view of a conventional actuator 40 adapted to drive a flow control valve as described above (refer to, for example, Japanese Patent Application Laid-Open No. H09-285100). The actuator 40 is constituted by a stepping motor and includes: stator yokes 41a and 42a coupled together so as to form a squared C-shape in axial cross section and to shape, in radial plan view, an annular configuration with a center hollow space c1 for housing a rotor assembly; stator yokes 41b and 42b coupled together in the same way as the stator yokes 41a and 42a; coil bobbins 43a and 43b formed by molding, having a squared C-shape cross section so as to form respective coil spaces a1 and b1 therein, and lodged inside respective squared C-shapes formed by the stator yokes 41a and 42a, and by the stator yokes 41b and 42b; coils 45a and 45b made of respective wound magnetic wires 44a and 44b and housed respectively in the coil spaces a1 and b1; a cup-like case 46 to house all the components described above; a lid plate 47 to cover the case 46; rubber packing members 48 and 49 sandwiched respectively between the stator yoke 42b and a bottom 46a of the case 46, and between the stator yoke 41a and the lid plate 47 with a bearing 58; and a rotary shaft 50 having a screw portion 50a formed toward its distal end.
FIG. 6 is a cross sectional view of a relevant portion of a gas meter incorporating the actuator of FIG. 5. The actuator 40 is fixedly attached to a frame 52 of the gas meter by screws 54 such that the screw portion 50a of the rotary shaft 50 is screwed into a center screw hole of a shutoff valve 51, and that a ring-like rubber packing member 53 is sandwiched between the lid plate 47 and the frame 52. A gas flow control is conducted such that the shutoff valve 51 is linearly moved upward (in the figure) by the rotation of the rotary shaft 50 and with guidance of a guide rod 59 and is brought in touch with a valve seat 56 so as to clog up an open mouth 57 of a gas channel 55 thereby shutting off gas flowing through the gas channel 55. Also, gas, which flows into the inside of the actuator 40 through a hole of the bearing 58, specifically through a gap between the bearing 58 and the rotary shaft 50, is shut off by the cup-like case 46, the lid plate 47, the coils 45a and 45b, and the rubber packing members 48 and 49 thus preventing the gas from leaking out.
FIG. 7 is a cross sectional view of another conventional actuator 60 and a gas meter incorporating the actuator 60 (refer to, for example, Japanese Patent Application Laid-Open No. H11-030356). The actuator 60 includes: a rotor 61 composed of a rotary shaft 62, a sleeve 63 having the rotary shaft 62 inserted through its center, and a magnet 64 disposed at the outer circumference of the sleeve 63 and provided with magnetic poles; a stator 65 having coils 66 and disposed outside the rotor 61 so as to have its inner circumferential surface oppose the magnetic poles of the magnet 64; a transmission unit 62a constituted by a screw which is formed at the outer circumferential surface of the rotary shaft 62 and which is adapted to screw together with a screw hole of a moving block 67; and a rotation stopper 68 adapted to prohibit the moving block 67 from rotating together with the rotary shaft 62. A flow control block 69 is connected to the moving block 67 so as to be movable in the axial direction, and is brought in touch with a valve seat 71 of a fluid channel 70 to thereby control the flow amount of fluid. A bulkhead 72 including a flange 72a is provided. The bulkhead 72 is made of a non-magnetic material, shaped into a circular hollow-cylinder with one end blinded, and hermetically partitions off the stator 65 from the rotor 61 and the flow control block 69 connected to the rotor 61 via the moving block 67. A mounting plate 73 is provided, to which the flange 72a of the bulkhead 72 and the stator 65 are attached. An O-ring 74 as a sealing unit is disposed between the flange 72a and the mounting plate 73, and an O-ring 75 as a sealing unit is disposed between a flange 70a of the fluid channel 70 and the mounting plate 73.
FIG. 8 is a cross sectional view of still another conventional actuator 80 and a gas meter incorporating the actuator 80 (refer to, for example, Japanese Patent Application Laid-Open No. 2003-322274). The actuator 80 is used as a solenoid valve and functions to press a valve plug against a valve seat for controlling the flow amount of fluid. The actuator 80 constituting a solenoid is disposed in a gas meter body 100, and activates a pilot valve 87 thereby controlling the flow amount of fluid. The solenoid (the actuator 80) includes: a sleeve 81 having its upper end portion engagingly fitted into a hole formed in the body 100; a plunger 82 disposed in the sleeve 81 so as to be movable in the axial direction; a core 83 shaped hollow-cylindrical and engagingly fitted in the lower end of the sleeve 81; a shaft 86 having its one end portion supported by a bearing 84 formed in the body 100 and the other end portion supported by a bearing 85 disposed in the hollow of the core 83; a spring 88 disposed between the plunger 82 and the bearing 85 and functioning to press the aforementioned pilot valve 87 by way of the shaft 86 for clog-up operation; a magnet coil 89 disposed outside the sleeve 81; a yoke 90 disposed so as to surround the magnet coil 89; and a plate 91 disposed around the sleeve 81 so as to form a magnetic circuit between the yoke 90 and the sleeve 81. The core 83 has its one open end clogged by an insert member 92, and then the tip ends of the core 83 and the insert member 92 are sealed up by a welded joint 92a. An O-ring 93 is disposed in an open space defined by the body 100, the sleeve 81, and the plate 91. The actuator 80 is fixed to the body 100 such that an end portion 90a of the yoke 90 is bent inward so as to catch a flange 100a of the body 100.
In the first example described with reference to FIGS. 5 and 6, the actuator 40 constituted by a stepping motor must be attached to the gas meter such that the actuator 40 is set to the gas meter, the ring-like rubber packing member 53 is put between the lid plate 47 and the frame 52, and the actuator 40 is fixed to the frame 52 of the gas meter by the screws 54 thus taking time for screwing work, which results in deterioration of workability. Also, if there is variance in tightening torque to drive the screws 54, gas flowing in the gas channel 55 can leak out through a gap possibly formed between the lid plate 47 and the frame 52. Further, since the position of the actuator 40 is shifted with respect to the axial direction according to the strength to tighten the screws 54, the axial play of the rotary shaft 50 cannot be duly controlled. And, gas which gets through a gap between the rotary shaft 50 and the bearing 58 and flows inside is supposed to be prevented from exiting out by means of members functioning as sealing unit, such as the case 46, the lid plate 47, the coils 45a and 45b, the rubber packing members 48 and 49, and the bearing 58, and it is difficult to coordinate so many members properly.
In the second example described with reference to FIG. 7, since a sealing structure is formed such that the O-ring 75 is disposed between the mounting plate 73 of the actuator 60 and the wall of the fluid channel 70, the mounting plate 73 must be screwed to the flange 70a of the fluid channel 70 thus taking time for screwing work, which results in deterioration of workability. And, if there is variance in tightening torque to drive the screws, it can happen that gas flowing in the gas channel leaks out through a gap possibly formed between the flange 70a of the fluid channel wall 70 and the mounting plate 73.
In the third example described with reference to FIG. 8, gas flowing into the inside of the actuator 80 through a gap between the bearing 84 and the shaft 86 is prevented from leaking out by the core 83 and the insert member 92 welded to the core 83, thus taking time for welding work to form the welded joint 92a, which results in deterioration of workability. And, the actuator 80 is fixed to the body 100 of the gas meter such that the end portion 90a of the yoke 90 is bent inward so as to catch the flange 100a formed at the bottom portion of the body 100, thus requiring dedicated tools for bending work, which hinders simple attachment and detachment of the actuator 80.